Datasheet

HVLED815PF Device description
Doc ID 023409 Rev 4 27/36
Ultimately, this will result in a low-frequency intermittent operation (hiccup-mode operation),
with very low stress on the power circuit. This special condition is illustrated in the timing
diagram of
Figure 21 .
Figure 21. Hiccup-mode OCP: timing diagram
4.11 High Power Factor implementation
Referring to the principle application schematic on Figure 1 , two contributions are added on
the CS pin in order to implement the high power factor capability (trough R
PF
resistor) and
keeping a good line-regulation (trough R
OS
resistor). The application schematic on Figure 1
is intended for a single range input voltage. For wide range application a different reference
schematic can be used; refer to the dedicated application note for further details.
Through the R
PF
resistor a contribution proportional to the input voltage is added on the CS
pin: as a consequence the input current is proportional to the input voltage during the line
period, implementing a high power factor correction. The contribution proportional to the
input voltage is generated using the auxiliary winding, as a consequence a diode in series to
the R
PF
resistor is needed.
Through the ROS resistor a positive contribution proportional to the average value of the
input voltage is added on the CS pin in order to keep a good line-regulation.
The voltage contribution proportional to the average value of the input voltage is generated
trough the low pass filter R
A
/R
B
resistor and C
OS
capacitor. A diode in series to the R
A
/R
B
resistor is suggested to avoid the discharge of C
OS
capacitor in any condition.
The R1 resistor between CS and SOURCE pin is needed to add on the CS pin also the
contribution proportional the output current trough the R
SENSE
resistor.
AM13571v1
VDS
VccON
Vcc
OFF
Vccrest
Secondary diode is shorted here
t
t
t
VCS
1 V
Two switching cycles
VCC
Vcsdis